Backlight assembly and liquid crystal display device having the same

ABSTRACT

There is disclosed a backlight assembly for maximizing a light incidence efficiency by changing a construction of a light guide plate and a liquid crystal display device having the same. A light incidence surface of the light guide plate receiving a light from a lamp is inclined to make an obtuse angle with a light-emitting surface through which the light is transferred to the display unit. An open surface of a lamp cover that is disposed to face towards the light incidence surface is formed to have the same inclined angle as the light incidence surface of the light guide plate. In addition, a light reflecting plate and an optical sheet are respectively disposed on the top and bottom surfaces of the light guide plate, on which light absorbing layers, for absorbing light that leaks from the light guide plate, are formed at both ends thereof. Accordingly, there are advantages in that the light incidence efficiency of the light is improved even though a thickness of the light guide plate is not increased, and that it is possible to remove the light concentrated at an edge of the light incidence surface of the light guide plate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device, andmore particularly, to a back light assembly for maximizing a lightincident efficiency by changing a structure of a light guide plate forguiding lights from a lamp to a display unit for displaying images and aliquid display device having the same.

2. Description of the Related Art

At the present time, information processing devices are rapidlydeveloping with trends towards various architectures, functions andfaster information processing speed. Information processed in theseinformation processing devices has an electrical signal format. In orderto visually confirm information processed in an information processingdevice, a display should be provided as an interface device. An exampleof such a display device is the liquid crystal display (LCD).

LCDs offer numerous advantages as display devices such as light weight,small size, high resolution, and low power consumption. They are alsoenvironmentally friendly and they offer a display of full colorscompared with the traditional cathode ray tube (CRT). Such advantagesallow the LCDs to replace the CRTs and to be recognized as a nextgeneration display.

LCDs apply electric power to liquid crystal having a specific molecularconfiguration so as to vary the molecular arrangement of the liquidcrystal. The variation in the molecular configuration of the liquidcrystal causes a variation in optical properties such as birefringence,optical rotary power, dichroism and light scattering. The LCDs utilizesuch variations in optical properties to display an image.

In the LCD device, functions of a backlight assembly bring attention toa more important problem. The reason is that the backlight assemblyaffects both the mechanical and optical characteristics of the LCDdevice such that the size and the light efficiency of the LCD deviceundergo a change. This is discussed, along with a description of priorart systems, in conjunction with FIGS. 1-3 below.

FIG. 1 is an exploded perspective view schematically showing the LCDdevice according to the conventional art schematically. FIG. 2 is asectional view schematically showing the constructions of a lamp unitand a light guide unit in the backlight assembly as shown in FIG. 1.FIG. 3 is a view showing a pathway of the light in the light guide plateshown in FIG. 2.

Referring first to FIG. 1, the LCD device 900 has a LCD module 700 fordisplaying images when image signals are applied thereto and a case (notshown) for receiving the LCD module 700. The LCD module 700 includes adisplay unit 710 having a LCD panel for showing the images.

The display unit 710 includes the LCD panel 712, a data-side printedcircuit board (PCB) 714, a gate-side PCB 717, a data-side tape carrierpackage 716 and a gate-side tape carrier package 718.

The LCD panel 712 includes a thin film transistor substrate 712 a, acolor filter substrate 712 b and liquid crystal (not shown) between thethin film transistor substrate 712 a and the color filter substrate 712b.

The thin film transistor substrate 712 a is a transparent glass on whichthe thin film transistors are formed in a matrix form. Data lines arerespectively connected with source terminals of the thin filmtransistors and gate lines are connected with gate terminals of the thinfilm transistors. Furthermore, pixel electrodes are respectively formedat drain terminals of the thin film transistors, which are made of atransparent conductive material such as Indium Tin Oxide (ITO).

The color filter substrate 712 b is provided to face the thin filmtransistor substrate 712 a. RGB pixels are formed on the color filtersubstrate 712 b by means of a thin film process, which presents apredetermined color while the light passes through the color filtersubstrate 712 b. Common electrodes made of the ITO are coated on thefront surface of the color filter substrate 712 b.

When the thin film transistors of the thin film transistor substrate 712a are turned on, an electric field is created between the pixelelectrodes of the thin film transistor substrate 712 a and the commonelectrodes of the color filter substrate 712 b. The electric fieldcauses the liquid crystal to change the array angle, which results inthe permeability of the light being changed. As a result, the desiredpixels are obtained.

A driving signal and a timing signal are applied to the gate lines anddata lines of the thin film transistor in order to control the arrayangle of the liquid crystal and the time of arraying the liquid crystalin the LCD panel 712. A source part for providing the data drivingsignal to the LCD panel 712 is formed on the data-side PCB 714, and agate part for providing the gate driving signal to the gate lines isformed on the gate-side PCB 717. In other words, the PCBs 714 and 717generate and apply the gate driving signal and the data signal fordriving the LCD device as well as a plurality of timing signals forapplying the gate driving signal and the data signal to the gate linesand the data lines of the LCD panel 712.

Continuing with FIG. 1, the backlight assembly 720 is provided under thedisplay unit 710 so as to uniformly supply the light to the display unit710. The backlight assembly 720 includes a lamp 721 for generating thelight. The lamp 721 is protected by means of a lamp cover 722.

The light guide plate 724 has a size corresponding to that of the liquidcrystal panel 712 of the display unit 710, which is disposed under theliquid crystal panel 712 to guide the light emitted by the lamp 721toward the display unit 710 by changing a pathway of the light.

A plurality of optical sheets is provided on the light guide plate 724so as to uniformly adjust the brightness of the light that transmittedfrom the light guide plate 724 to the LCD panel 712. In addition, alight reflecting plate 728 is provided under the light guide plate 724to reflect the light, which is leaked from the light guide plate 724,towards the light guide plate 728 so as to improve the efficiency of thelight.

The display unit 710 and the backlight assembly 720 are supported bymeans fo a mold frame 820 used as a receptacle. The mold frame 820 isprovided with a chassis 810 for preventing the display unit 710 fromdeparting from the mold frame 820 while the data-side PCB 714 and thegate-side PCB 7171 are bent towards the outside of the mold frame 820and are fixed to the bottom surface of the mold frame 820.

Referring now to FIG. 2, the light guide plate 724 is of an edge-typehaving a uniform thickness, and a lamp 721 for supplying the light isprovided at an end of the light guide plate 724. Typically, the lightemitted from the lamp 721 of the edge-type light guide plate 724 istransmitted through a pathway as shown in FIG. 3.

As shown in FIG. 3, the light emitted from the lamp 721 is transmittedto the top and bottom surfaces 724 a and 724 b of the light guide plate724 according to the incidence angle thereof. A part of the lighttransmitted to the top surface 724 a of the light guide plate 724 isprovided to the display unit 710 after passing through the top surface724 a of the light guide plate 724, while the remainder of the light isreflected at the bottom surface 724 b of the light guide plate 724 andthen transmitted toward the top surface 724 a of the light guide plate724.

Meanwhile, the light transmitted to the bottom surface 724 b of thelight guide plate 724 is reflected by means of printed patterns (notshown) that are formed on the bottom surface 724 b of the light guideplate 724, and then the light passes through the top surface 724 a ofthe light guide plate 724. Ultimately, the light is provided to thedisplay unit 710. At this time, a part of the light transmitted to thebottom surface 724 b of the light guide plate 724 passes through thebottom surface 724 b and leaks out of the light guide plate 724.However, the leaked light is reflected to the display unit 710 by meansof the light reflecting plate 728 that is disposed between the lightguide plate 724 and the mold frame 820 (see FIG. 1).

With relation to the light guide plate 724, the brightness of the lightthat is supplied to the display unit 710 increases in proportion to thethickness of the light guide plate 724. Accordingly, a method ofincreasing the thickness of the light guide plate 724 can be adopted tomaximize the incidence efficiency of the light. When the thickness ofthe light guide plate 724 increases, however, there is a problem in thatthe LCD device becomes heavier and has an increased thickness.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above-mentionedproblem, and accordingly it is an object of the present invention toprovide a backlight assembly for maximizing a light incidence efficiencyby changing a construction of a light guide plate for guiding lightsfrom a lamp to a display unit for displaying images.

It is another object of the present invention to provide a liquidcrystal display (LCD) device having a backlight assembly for maximizinga light incidence efficiency.

To achieve the first object of the present invention, a backlightassembly according to the present invention has a light guiding unitthat guides light provided through a light incidence surface to adisplay unit in order to display images, the light incidence surfacebeing formed to make an obtuse angle with a light-emitting surfacethrough which the light is emitted to the display unit. A light emittingunit is disposed on the light incidence surface of the light guidingunit to emit and provide the light through the light incidence surfaceto the light guiding unit.

To achieve the second object of the present invention, a LCD deviceaccording to the present invention has a display unit for displayingimages and a light guiding unit, the light incidence surface is formedto make an obtuse angle with a light-emitting surface through which thelight is emitted to the display unit for guiding light provided throughthe light incidence surface to the display unit. A light emitting unitis mounted on the light incidence surface of the light guiding unit toemit and provide the light through the light incidence surface to thelight guiding unit, and a light reflecting unit is disposed on thebottom surface of the light guiding unit to reflect the light, whichleaks from the light guiding unit, toward the display unit.

Meanwhile, the light emitting unit includes at least one lamp foremitting the light and a lamp cover for covering and protecting thelamp. The lamp cover is mounted on the light incidence surface of thelight guiding unit, which has an open side in order that the lightemitted from the lamp is transmitted through the open side to the lightguiding unit. The open side of the lamp cover is declined at aninclination angle equal to an inclination angle of the light incidencesurface or formed to be parallel with a backside opposite to the openside thereof. The light incidence surface has a length as 1.2 to 1.8times as that of the outer diameter of the lamp.

Furthermore, a printed pattern is formed on a bottom surface of thelight guiding unit to reflect the light transmitted from the lamp towardthe display unit. This pattern has a higher density according as theprinted pattern is located farther away from the light incidence surfaceof the light guiding means

A light reflecting plate and an optical sheet, on which a lightabsorbing layer is formed to absorb the light leaked from the lightguiding unit, are mounted on the top and the bottom surfaces of thelight guiding unit. In a preferred embodiment, a diffusion plate fordiffusing the light, or a prism for concentrating the light, is used asthe optical sheet. A length of a shortest distance from an apex of theobtuse corner of the light incidence surface to the bottom surface ofthe light guiding unit is substantially equal to a diameter of the lamp.

In the backlight assembly and the LCD device according to the presentinvention, as the light incidence surface of the light guide plate isdeclined at the obtuse angle with the top surface of the light guideplate, the light incidence efficiency can be improved even though thethickness of the light guide plate is not increased.

In addition, it is possible to absorb and remove the light concentratedat a corner portion of the light incidence surface of the light guideplate by means of the light absorbing layer formed on a predeterminedportion of the light reflecting plate, the light diffusing plate and/orthe light guide plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and other advantages of the present invention willbecome more apparent by describing in detail preferred embodimentsthereof with reference to the attached drawings, in which:

FIG. 1 is an exploded perspective view schematically showing aconventional liquid crystal display device;

FIG. 2 is a sectional view showing the structures of a lamp unit and alight guide unit of a backlight assembly as shown in FIG. 1;

FIG. 3 is a view showing a light guide pathway of the light guide unitshown in FIG. 2;

FIG. 4 is an exploded perspective view schematically showing a liquidcrystal display device according to a preferred embodiment of thepresent invention;

FIGS. 5 and 6 are views showing constructions of the lamp unit and thelight guide unit of the backlight assembly shown in FIG. 4;

FIG. 7 is a view showing the constructions of the lamp and the lightguide plate of the backlight assembly particularly shown in FIG. 6;

FIGS. 8 and 9 are views showing a light diffusing plate and a lightreflecting plate of the light guide unit shown in FIG. 6;

FIG. 10 is a view showing a printed pattern of the light guide plateshown in FIG. 6;

FIG. 11 is a view showing the printed pattern and an absorbing layer ofthe light guide plate shown in FIG. 6;

FIGS. 12 and 13 are views showing a light incidence surface of the lightguide plate and a length and an installed position of the lamp shown inFIG. 6;

FIG. 14 is a view showing a construction in that plural lamps areadopted to the backlight assembly shown in FIG. 6;

FIGS. 15 and 16 are views showing another construction of the lamp unitand the light guide unit of the backlight assembly shown in FIG. 4;

FIG. 17 is a view showing a length of the light incidence surface of thelight guide plate and the lamp shown in FIG. 16, respectively; and

FIGS. 18A to 18E are views showing light guide plates according to thepresent invention, in which the light guide plates having a differentstructure from one another respectively provide pathways for the light.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, preferred embodiments of the present invention will beexplained in detail with reference to the attached drawings.

FIG. 4 is an exploded perspective view schematically showing a liquidcrystal display device according to a preferred embodiment of thepresent invention.

Referring first to FIG. 4, the liquid crystal display (LCD) device 100includes a LCD module 200, for displaying images when image signals areapplied to the LCD module 200, as well as front and rear cases (notshown) for receiving the LCD module 200.

The LCD module 200 includes a display unit 210 having a LCD panel 212for displaying the images.

The display unit 210 includes a LCD panel 212, a data-side PCB 214, adata-side tape carrier package 216, a gate-side PCB 217 and a gate-sidetape carrier package 218.

The LCD panel 212 has a thin film transistor substrate 212 a, a colorfilter substrate 212 b and a liquid crystal (not shown) between the thinfilm transistor substrate 212 a and the color filter substrate 212 b.

The thin film transistor substrate 212 a is a transparent glasssubstrate on which thin film transistors in matrix are formed. A dataline is connected with a source terminal of the thin film transistorsand a gate line is connected with a gate terminal of the thin filmtransistors. Furthermore, pixel electrodes made of ITO as a transparentand conductive material are formed in a drain terminal of the thin filmtransistors.

When electric signals are applied to the data line and to the gate line,the electric signals are inputted into the source terminal and the gateterminal of the respective thin film transistors. As the electricsignals are inputted to the thin film transistors, the thin filmtransistors are respectively turned-on or turned-off, resulting inoutputting the electric signals that is required to form pixels to thedrain terminals.

The color filter substrate 212 b is provided to face to the thin filmtransistor substrate 212 a. The color filter substrate 212 b has RGBpixels that are formed by a thin film process to present desired colorswhile the light is passing through the color filter substrate 212 b. Asurface of the color filter substrate 212 b is covered with commonelectrodes made of ITO.

As described above, when the electricity is applied to the gate andsource terminals of the transistor on the thin film transistor substrate212 a to turn on the thin film transistor, an electric field is formedbetween the pixel electrodes and common electrodes of the color filtersubstrate 212 b. The arranging angle of the liquid crystal injectedbetween the thin film transistor substrate 212 a and the color filtersubstrate 214 b is changed by the electric field, and a lightpenetrating degree is changed as the arranging angle is changed so as toproduce a wanted pixel.

In order to control the time at which the arranging angle of the liquidcrystal of the LCD panel 212, a driving signal and a timing signal areapplied to the gate line and to the data line of the thin filmtransistor.

As shown in FIG. 4, the data-side tape carrier package 216, which is aflexible circuit board, is attached to the source portion of the LCDpanel 212 to decide a time of applying a data driving signal. On theother hand, the gate-side tape carrier package 218 is attached to thegate portion of the LCD panel 212 to decide a time of applying agate-driving signal.

The data-side PCB 214 and the gate-side PCB 217, which respectivelyapply the driving signal to the gate line and to the data line as soonas they receive image signals input from outside of the LCD panel 212,make contact with the data-side tape carrier package 216 for the dataline and the gate-side tape carrier package 218 for the gate line in theLCD panel 212, respectively. A source part is formed on the data-sidePCB 214, which receives the image signals from an exterior informationprocessing device (not shown) such as a computer, and then provides thedata driving signal to the LCD panel 212. Also, a gate part is formed onthe gate-side PCB 217, which receives the image signals, and providesthe gate driving signal to the gate line of the LCD panel 212.

In other words, the data-side PCB 214 and the gate-side PCB 217 generatethe data driving signal and the gate signal for driving the LCD deviceand the plural timing signals for applying the gate driving signal andthe data signal in an acceptable time, so as to apply the gate drivingsignal through the gate-side tape carrier package 218 to the gate lineof the LCD panel 212 and the data signal through the data-side tapecarrier package 216 to the data line of the LCD panel 212.

A backlight assembly 220 is disposed under the display unit 210 so as touniformly supply the light to the display unit 210. The backlightassembly 220 includes first and second lamps 221 a and 221 b forgenerating the light. The first and second lamps 221 a and 221 b arerespectively covered with first and second lamp covers 222 a and 222 b.Furthermore, the backlight assembly 220 may have at least one lampproviding the light. Further details relating to the lamps will bedescribed hereinafter.

A light guide plate 224 has a size corresponding to that of the LCDpanel 212 of the display unit 210 and is disposed under the LCD panel212 so as to guide the light generated by the first and second lamps 221a and 221 b towards the display unit 210 while changing the pathway ofthe light. In FIG. 4, the light guide plate 224 is depicted as anedge-type plate having a uniform thickness along its length exceptingfor both ends. The first and second lamps 221 a and 221 b are mounted atboth ends of the light guide plate 224 to increase a light efficiency.

In addition, both ends of the light guide plate 224 are respectivelyformed in that a light incidence surface through which the light fromthe first and second lamps 221 a and 221 b is formed to be at an obtuseangle with a light-emitting surface (i.e., the top surface). The lightguide plate 224 will be described in detail below with reference to thedrawings.

Meanwhile, a plurality of optical sheets is disposed on the light guideplate 224 so that a brightness of the light emitted from the light guideplate 224 to the LCD panel 212 may be uniformly formed. Furthermore, alight reflecting plate 228 is provided under the light guide plate 224in order to reflect the leaked light to the light guide plate 224,resulting in increased light efficiency.

The display unit 210 and the backlight assembly 220 are supported andfixed by means of a mold frame 400 that is used as a receptacle. Achassis 330 for preventing the display unit 210 from departing from themold frame 400 is provided above the display unit 210 while thedata-side PCB 214 and the gate-side PCB 217 are bent towards the outsideof the mold frame 400 and are fixed to the bottom surface of the moldframe 400.

FIG. 5 is a view for showing constructions of the lamp unit and thelight guide plate of the backlight assembly shown in FIG. 4, and FIG. 6is a view for showing a construction of the light guide plate in FIG. 5,on which the optical sheet and the light reflecting plate are mounted.

Referring now to FIGS. 5 and 6, the first and second light incidencesurfaces 224 a and 224 b of the light guide plate 224, through which thelight is inputted from the first and second lamp 221 a and 221 b, aredeclined so that apexes of both ends of the light guide plate 224respectively are made at obtuse angle. In other words, the light guideplate 224 disposed between the first and second lamps 221 a and 221 bhas a shorter length on the top surface than that of the bottom surfacethereof.

Similarly, the first and second lamp covers 222 a and 222 b, whichprotect the first and second lamps 221 a and 221 b and reflect the lightfrom the first and second lamps 221 a and 221 b to the first and secondlight incidence surfaces 224 a and 224 b of the light guide plate, havea construction in that an open surface facing to the first and secondlight incidence surfaces 224 a and 224 b is not matched with a lightreflecting surface opposite thereto. That is, the open surfaces of thefirst and second lamp covers 222 a and 222 b contacting to the first andsecond light incidence surfaces 224 a and 224 b are respectivelydeclined to be in parallel with the first and second light incidencesurfaces 224 a and 224 b. The light reflecting surfaces facing to theopen surfaces of the first and second lamp covers 222 a and 222 b, toreflect the light emitted from the first and second lamps 221 a and 221b to the light guide plate 224, intersect the top and bottom surfaces ofthe light guide plate 224. To the contrary, the top surfaces of thefirst and second lamp covers 222 a and 222 b, respectively covering thefirst and second lamps 221 a and 221 b, have a wider width than that ofthe bottom surfaces thereof.

FIG. 7 is a view for showing the structures of the lamp and the lightguide plate of the backlight assembly particularly shown in FIG. 6.

Referring now to FIG. 7, the light reflecting plate 228 is disposedunder the light guide plate 224, and the optical sheet 226 a, such as adiffusion plate or a prism, is mounted on the light guide plate 224. Thelight reflecting plate 228 basically carries out reflecting the lightleaked from the light guide plate 224 while the optical sheet 226 adiffuses or concentrates the light emitted from the light guide plate224. That is, in the case that a diffusion sheet is used as the opticalsheet 226 a, the sheet can scatter and diffuse the light emitted fromthe light guide plate 224, while, on the other hand, in the case that aprism sheet is used as the optical sheet 226 a, the sheet canconcentrate the light emitted from the light guide plate 224 to improvethe brightness of the light at a front of the LCD panel.

A light absorbing layer is formed at both ends of each light reflectingplate 228 and optical sheet 226 a, i.e., at portions adjacent to thefirst and second light incidence surface 224 a and 224 b of the lightguide plate 224 so as to absorb the light from the light guide plate224, as shown in FIGS. 7 to 11.

FIG. 7 is a view showing the structures of the lamp and the light guideplate of the backlight assembly particularly shown in FIG. 6, and FIGS.8 and 9 are views showing the optical sheet and the light reflectingplate of the light guide unit shown in FIG. 6. Also, FIG. 10 is a viewshowing a printed pattern of the light guide plate shown in FIG. 6, andFIG. 11 is a view showing the printed pattern and the light absorbinglayer of the light guide plate shown in FIG. 6.

Generally, without relation to a construction of ends of the light guideplate 224, there is presented an appearance in that the light isconcentrated at a corner portion of the light guide plate 224 in anedge-type LCD device. To prevent the light from concentrating, it ispreferred to quickly leak and remove the concentrated light at thecorner portion of the light guide plate 224. The light absorbing layers228 a, 228 b, 226 b, 226 c, 227 a and 227 b are formed to absorb thelight at both ends of any one of the light reflecting plate 228, theoptical sheet 226 a and the light guide plate 224 (i.e., at portionsadjacent to the first and second light incidence surfaces 224 a and 224b, as shown in FIGS. 8 and 9).

Meanwhile, fine printed patterns 225 a, 225 b and 225 c, as shown inFIG. 10, are formed on the bottom surface of the light guide plate 224to reflect the light provided by the first and second lamps 221 a and221 b to the display unit 210, thereby resulting in increasing thereflection efficiency.

The printed patterns 225 a, 225 b and 225 c are formed to be graduallymuch more dense from the both end portions to a center portion of thelight guide plate 224. That is, a space between the printed patterns 225b and 225 c is gradually wider as the patterns more closely approach thefirst and second light incidence surface 224 a and 224 b of the lightguide plate 224. The reason for forming the printed pattern 225 a, 225 band 225 c such that each has a different space than another, asdescribed above, is as follows.

First, there is presented an appearance in that the light is generallyconcentrated not only at the light guide plate 224 that is declined atboth ends but also at corner portions of the first and second lightincidence surfaces 224 a and 224 b of the light guide plate 224 in anedge-type LCD device. The light absorbing layers 226 b, 226 c, 228 a,228 b, 227 a and 227 b are formed at both ends of the optical sheet 226a, the light reflecting plate 228 or the light guide plate 224 to removethe light concentrated at the corners of the first and second lightincidence surfaces 224 a and 224 b, as shown in FIGS. 8, 9 and 11. Theprinted patterns 225 a, 225 b and 225 c, which are formed on the bottomsurface of the light guide plate 224, carry out reflecting the lighttransmitted toward the bottom surface of the light guide plate 224 tothe display unit 210. Accordingly, it is preferred to leak and removethe light, which is concentrated at the corner portions of the first andsecond light incidence surfaces 224 a and 224 b and that is positionedout of an activation area of the display unit 210, through the bottomsurface of the light guide plate 224. As shown in FIG. 10, therefore, inthe area of the first and second light incidence surfaces 224 a and 224b of the light guide plate 224, it is preferred that the printedpatterns 225 b and 225 c have a wider space than the printed pattern 225a at the center portion of the light guide plate 224.

Up to now, the description has focused on the case that the lamps foremitting the light are mounted at both ends of the light guide plate224. In the case that the light incidence surface of the light guideplate 224 is declined, however, the printed patterns on the bottomsurface of the light guide plate 224 preferably have different spaceswith one other according to the area of the light guide plate 224 eventhough the lamp is only mounted at an end of the light guide plate 224,as described above. For example, when the first lamp 221 a is disposedat an end of the light guide plate 224, the spaces of the printedpatterns are gradually narrower in a direction in which the light fromthe first lamp 221 a is transmitted from the first light incidencesurface 224 a to the declined surface opposite to the first lightincidence surface 224 b.

As shown in FIG. 11, when the light absorbing layers 227 a and 227 b aredirectly formed on the light guide plate 224, it is possible not to formthe printed patterns in the area of the first and second light incidencesurfaces 224 a and 224 b of the light guide plate 224. However, theprinted pattern 225 is formed in an area of the light guide plate 224 inwhich the light absorbing layers 227 a and 227 b are not formed, so asto reflect the light emitted by the first and second lamps 221 a and 221b toward the light guide plate 224, as shown in FIG. 11.

Referring now to FIG. 12, the declined portions of the first and secondlight incidence surfaces 224 a and 224 b of the light guide plate 224are 1.2 to 1.8 times larger in length than an outer diameter of thefirst and second lamps 221 a and 221 b. As described above, when theratio of the length of the declined surface in the first and secondlight incidence surfaces 224 a and 224 b to the outer diameter of thefirst and second lamps 221 a and 221 b is held to become 1.2 to 1through 1.8 to 1, with reference to FIG. 13, a line that extends fromthe center point of the first and second lamps 221 a and 221 b to benormal to the first and second light incidence surfaces 224 a and 224 bintersects the first and second light incidence surfaces 224 a and 224 bbeneath the center point (“CP”) of the first and second light incidencesurfaces 224 a and 224 b.

On the other hand, continuing with FIG. 12, if the thickness of thelight guide plate 224 is more thinner and the inclination of the firstand second surfaces 224 a and 224 b is more sluggish, the ratio of thethickness “Lt” of the light guide plate 224 to the outer diameter “r” ofthe first and second lamps 221 a and 221 b substantially can approach 1to 1.

Though not shown in drawings, a wedge-type light guide plate can beadapted to the LCD device, in which the thickness of the plate isgradually thinner in a direction from a light incidence surface in whichthe light emitted by the lamp is transmitted to an end opposite to thelight incidence surface. While the lamp is generally disposed at an endportion wherein the thickness of the light guide plate is large, such asin the case of the wedge-type light guide plate, at least one lamp ismounted at the end portion. Therefore, as the light incidence surface ofthe end portion at which the lamp of the light guide plate is disposedis made declined, it is possible to improve the light incidenceefficiency. In addition, the light absorbing layer can be formed at oneof the light guide plate, the light reflecting plate, which is mountedon the bottom surface of the light guide plate, and the optical sheet,such as a diffusion plate or a prism sheet, which is mounted on the topsurface of the light guide plate, as shown in FIGS. 8 to 11. Thedeclined portion in the light incidence surface of the wedge-type lightguide plate preferably has about 1.2 to 1.8 times in length than doesthe outer diameter of the lamp. The thickness from an obtuse apex of thelight incidence surface to the bottom surface of the wedge-type lightguide plate substantially is the same size as that of the outer diameterof the lamp.

FIG. 14 is a view showing a construction in that plural lamps areadopted to the backlight assembly shown in FIG. 6. Hereinafter, the likereference numerals are adopted to the elements having the same functionsas that of the structure element in FIG. 7.

Referring now to FIG. 14, the first and third lamps 221 a and 223 a, andthe second and fourth lamps 221 b and 223 b are respectively mounted atboth ends of the light guide plate 224. The first and second lightincidence surfaces 224 a and 224 b of the light guide plate 224 aredeclined as shown in FIG. 6. The first and second lamp covers 222 a and222 b respectively protecting the first and third lamps 221 a and 223 aand the second and fourth lamps 221 b and 223 b have opened surfaceswhich are declined at the same angle as that of the first and secondlight incidence surfaces 224 a and 224 b. In addition, the lightabsorbing layer can be formed at one of the light guide plate 224, thelight reflecting plate 228, which is mounted on the bottom surface ofthe light guide plate 224, and the optical sheet 226 a, such as adiffusion plate or a prism sheet, which is mounted on the top surface ofthe light guide plate 224, as shown in FIGS. 8 to 11. The declinedportion in the first and second light incidence surfaces 224 a and 224 bof the light guide plate 224 preferably is 1.2 to 1.8 times in lengththan the outer diameter of the first, second, third and fourth lamps 221a, 221 b, 223 a and 223 b.

Hereinafter, another construction of the lamp unit in the backlightassembly as shown in FIG. 4 will be described.

FIG. 15 is a view showing another construction of the lamp unit and thelight guide unit in the backlight assembly shown in FIG. 4, and FIG. 16is a view showing another construction of the light guide unit in whicha diffusion plate and a light reflecting plate are mounted as shown inFIG. 15. FIG. 17 is a view showing each length of a light incidencesurface of the light guide plate and the lamp shown in FIG. 15. In FIGS.15 to 17, the like reference numerals are respectively adapted to theelements having the same construction and function as those of theelements shown in FIGS. 5 to 12.

Referring now to FIGS. 15 and 16, the first and second light incidencesurfaces 224 a and 224 b of the light guide plate 224, in which thelight is transmitted, is declined at an obtuse angle with the topsurface of the light guide plate 224. In other words, the top surface ofthe light guide plate 224 is narrower than the bottom surface of thelight guide plate 224.

The open surface of the third and fourth lamp covers 222 c and 222 d,which protect the first and the second lamps 221 a and 221 b and reflectthe light emitted from the first and second lamps 221 a and 221 b towardthe light guide plate 224, are declined to be parallel with the firstand second light incidence surfaces 224 a and 224 b. Furthermore, alight reflecting surface, for reflecting the light emitted from thefirst and second lamps 221 a and 221 b toward the light guide plate 224,is formed to be parallel with and opposite to the open surface of thethird and fourth lamp covers 223 a and 223 b.

Referring now to FIG. 16, the light reflecting plate 228 is mountedunder the light guide plate 224, and the optical sheet 226 a, such asthe light diffusing plate or the prism sheet, is disposed on the lightguide plate 224. The light absorbing layer is formed in some area of thelight reflecting plate 228 and the optical sheet 226 a that is adjacentto the first and second light incidence surfaces 224 a and 224 b of thelight guide plate 224 as shown in FIGS. 8 and 9. The descriptionsrelating to the functions of the light reflecting plate 228 and theoptical sheet 226 a and the light absorbing layers 228 a, 228 b, 226 band 226 c has been described above with reference to FIGS. 7 to 9.

Meanwhile, the fine printed patterns 225 a, 225 b and 225 c as shown inFIG. 9 are formed on the bottom surface of the light guide plate 224 toincrease the reflection efficiency of reflecting the light emitted fromthe first and second lamps 221 a and 221 b toward the display unit 210.As shown in FIG. 10, the printed patterns 225 a, 225 b and 225 c are hasa higher density according as the printed pattern is located fartheraway from the light incidence surface of the light guiding means.

If the light absorbing layers 227 a and 227 b are directly formed on thelight guide plate 224, the printed patterns may not be formed in an areaof the first and second light incidence surfaces 224 a and 224 b of thelight guide plate 224, as shown in FIG. 11. In the area on which thelight absorbing layers 227 a and 227 b are not formed in the light guideplate 224, the printed pattern 225 is formed to reflect the lightemitted from the lamps 221 a and 221 b toward the light guide plate 224,as shown in FIG. 10.

Referring now to FIG. 17, the declined portions of the first and secondlight incidence surfaces 224 a and 224 b of the light guide plate 224are 1.2 to 1.8 times in length (“L”) than the outer diameter “r” of thefirst and second lamps 221 a and 221 b. On the other hand, if thethickness of the light guide plate 224 is thinner and the inclination ofthe first and second surfaces 224 a and 224 b is more sluggish, theratio of the thickness “Lt” of the light guide plate 224 to the outerdiameter “r” of the first and second lamps 221 a and 221 b substantiallycan be about 1 to 1 (see FIG. 12).

Table 1 presents a light incidence efficiency according to theconstruction of the light incidence surface of the light guide plate.

TABLE 1 Type A B C Means of flux  4133.11 5061.01 6010.9 (Im/m²)Comparison 100% 122.45% 145.43%

In Table 1, a type “A” is the light guide plate having the lightincidence surface perpendicular to the top and bottom surfaces of thelight guide plate. Type “B” is the light guide plate having the lightincidence surface that is declined at a preferred angle such that thetop surface is narrower in width than the bottom surface and the opensurface of a lamp cover is asymmetric to a light reflecting surfaceopposite to the open surface. Type “C” is the light guide plate havingthe light incidence surface that is declined at a preferred angle suchthat the top surface is narrower in width than the bottom surface andthe open surface of the lamp cover is parallel with the light reflectingsurface opposite to the open surface.

Referring now to Table 1, it can be noted that the light incidenceefficiency of the light guide plate is improved up to 22.45% incomparison with the light guide plate of the type “A” when the lightincidence surface of the light guide plate is declined in a manner ofthe type “B.” Furthermore, if the open surface of the lamp cover and thelight reflecting surface are formed to be symmetric in a manner of thetype “C,” the light incidence efficiency is improved even more.

FIGS. 18A to 18E are views showing the light guide plates according tothe present invention in which the light guide plates having a differentstructure with respect to each other provide pathways for the light.

FIGS. 18A and 18B show the light guide plate having a swallow-tail shapeat both ends, in which the light incidence surfaces are respectivelydepressed in a V-shape and a U-shape, respectively. FIG. 18C is thelight guide plate in which the top surface is wider than the bottomsurface and in which the light incidence surface is declined at apreferred angle. In FIGS. 18A to 18C, the light is leaked orconcentrated at the corners of the light incidence surface. FIG. 18Dshows the light guide plate having a uniform thickness over the entirewidth. In that case, however, the light guide plate has lower lightincidence efficiency than the light guide plate having the lightincidence surface that is declined. FIG. 18E shows the light guide plateaccording to the present invention in which the light leaked at thecorner of the light incidence surface is absorbed by the light absorbinglayers that is adhered to the light reflecting plate, thereby resultingin minimizing the concentration of the light.

In the backlight assembly and the LCD device according to the presentinvention, the top surface of the light guide plate, in which the lightfrom the lamps is emitted, is declined at an obtuse angle with the lightincidence surface of the light guide plate in which the light from thelamps is inputted. Accordingly, even though the thickness of the lightguide plate is not increased, the incidence efficiency of the light canbe improved.

Furthermore, the light reflecting plate is mounted under the bottomsurface of the light guide plate and the optical sheet is disposed onthe top surface of the light guide plate. In addition, because the lightabsorbing layer is formed at the ends of the light guide plate, thelight reflecting plate and/or the optical sheet acts to absorb the lightconcentrated at the corner of the light incidence surface.

Therefore, it is possible to remove the light concentrated at the cornerof the light incidence surface in the light guide plate efficiently,thereby improving the incidence efficiency of the light from the lampsand the quality of images displayed on the display unit.

Although the preferred embodiments of the present invention have beendescribed, it is understood that the present invention should not belimited to these preferred embodiments but various changes andmodifications can be made by one skilled in the art within the spiritand scope of the present invention as hereinafter claimed.

What is claimed is:
 1. A backlight assembly comprising: light guidingmeans for guiding a light provided through a light incidence surface toa display unit in order to display an image, the light incidence surfacebeing formed to make an obtuse angle with a light-emitting surfacethrough which the light is emitted to the display unit; and lightemitting means for emitting and providing the light through the lightincidence surface to the light guiding means, the light emitting meansbeing disposed on the light incidence surface of the light guidingmeans.
 2. A backlight assembly of claim 1, wherein the light emittingmeans comprises: at least one lamp for generating the light; and a lampcover to protect the lamp, the lamp cover being disposed on the lightincidence surface of the light guiding means and being open at a side inorder to emit the light from the lamp toward the light guiding means,and the open side of the lamp cover being declined at an inclinationangle equal to an inclination angle of the light incidence surface.
 3. Abacklight assembly of claim 2, wherein the open side of the lamp coveris formed to be parallel with a backside opposite to the open side ofthe lamp cover.
 4. A backlight assembly of claim 2, wherein the lightincidence surface has 1.2 to 1.8 times a length of an outer diameter ofthe lamp.
 5. A backlight assembly of claim 4, wherein the light guidingmeans has a thickness as large as the outer diameter of the lamp.
 6. Abacklight assembly of claim 2, wherein a printed pattern is formed at abottom surface of the light guiding means to reflect the light from thelamp toward the display unit.
 7. A backlight assembly of claim 6,wherein the printed pattern has a higher density according as theprinted pattern is located farther away from the light incidence surfaceof the light guiding means.
 8. A backlight assembly of claim 2, whereina light absorbing layer is formed on a bottom surface of the lightguiding means to absorb a part of the light emitted by the lamp.
 9. Abacklight assembly of claim 8, wherein the light absorbing layer isformed at a portion adjacent to the light incidence surface on thebottom surface of the light guiding means.
 10. A backlight assembly ofclaim 1, further comprising: light reflecting means for reflecting alight, which leaks from the light guiding means, toward the lightguiding means, the light reflecting means being disposed on a bottomsurface of the light guiding means; and an optical sheet for controllinga brightness of the light emitted from the light guiding means, theoptical sheet being disposed on a top surface of the light guidingmeans.
 11. A backlight assembly of claim 10, wherein a light absorbinglayer is formed on the light reflecting means and on the optical sheetso as to absorb the light that leaks from the light guiding means.
 12. Abacklight assembly of claim 11, wherein the optical sheet is a diffusionsheet or a prism sheet.
 13. A backlight assembly of claim 2, wherein thelight guiding means is a wedge-type light guide plate in which athickness of the plate varies so that the plate gradually becomesthinner according to being closer to an end portion of the light guidingmeans, the end portion being opposite to the light incidence surfacethrough which the light of the light emitting means is incident.
 14. Abacklight assembly of claim 13, wherein a length of a shortest distancefrom an apex of the obtuse corner of the light incidence surface to thebottom surface of the light guiding means is substantially equal to anouter diameter of the lamp.
 15. A liquid crystal display devicecomprising: a display unit for displaying an image; a light guiding unitfor guiding a light provided through a light incidence surface to thedisplay unit, the light incidence surface being formed to make an obtuseangle with a light-emitting surface through which the light is emittedto the display unit; and a light emitting unit for emitting andproviding the light through the light incidence surface to the lightguiding unit, the light emitting unit being mounted on the lightincidence surface of the light guiding unit; and a light reflecting unitfor reflecting a light, which leaks from the light guiding unit, towardthe display unit, the light reflecting unit being disposed on a bottomsurface of the light guiding unit.
 16. A liquid crystal display deviceof claim 15, wherein the light emitting unit comprises: at least onelamp for emitting the light; and a lamp cover to protect the lamp, thelamp cover being mounted on the light incidence surface of the lightguiding unit with a side thereof being open so that the light emittedfrom the lamp is emitted through the open side of the lamp cover to thelight guiding unit, and the open side of the lamp cover being declinedat an inclination angle equal to an inclination angle of the lightincidence surface.
 17. A liquid crystal display device of claim 16,wherein the open side of the lamp cover is formed to be parallel with abackside opposite to the open side thereof.
 18. A liquid crystal displaydevice of claim 17, wherein the light incidence surface has 1.2 to 1.8times a length of an outer diameter of the lamp.
 19. A liquid crystaldisplay device of claim 18, wherein a thickness of the light guidingunit at a position perpendicular to the light-emitting surface thereofis equal to the outer diameter of the lamp.
 20. A liquid crystal displaydevice of claim 16, wherein a printed pattern has a higher densityaccording as the printed pattern is located farther away from the lightincidence surface of the light guiding means.
 21. A liquid crystaldisplay device of claim 20, wherein the printed pattern has a higherdensity according as the printed pattern is located farther away fromthe light incidence surface of the light guiding unit.
 22. A liquidcrystal display device of claim 16, wherein a light absorbing layer isformed on a bottom surface of the light guiding unit to absorb a part ofthe light emitted by the lamp.
 23. A liquid crystal display device ofclaim 22, wherein the light absorbing layer is formed at a portionadjacent to the light incidence surface on the bottom surface of thelight guiding unit.
 24. A liquid crystal display device of claim 15,further comprising an optical sheet for diffusing the light emitted fromthe light guiding unit, the optical sheet being disposed on a topsurface of the light guiding unit.
 25. A liquid crystal display deviceof claim 24, wherein a light absorbing layer is formed on the lightreflecting unit and on the optical sheet so as to absorb the light thatleaks from the light guiding unit.
 26. A liquid crystal display deviceof claim 25, wherein the optical sheet is a diffusion sheet or a prismsheet.
 27. A liquid crystal display device of claim 16, wherein thelight guiding unit is a wedge-type light guide plate in which athickness of the plate varies so that the plate gradually becomesthinner according to being closer to an end portion of the light guidingmeans, the end portion being opposite to the light incidence surfacethrough which the light of the light emitting means is incident.
 28. Aliquid crystal display device of claim 27, wherein a length of shortestdistance from an apex of the obtuse corner of the light incidencesurface to the bottom surface of the light guiding unit is substantiallyequal to an outer diameter of the lamp.
 29. The backlight assembly ofclaim 1, wherein the light incidence surface and the light emittingsurface are substantially flat surfaces.
 30. A liquid crystal displaydevice comprising: a display unit that displays an image; a lightguiding unit that guides a light provided through a light incidencesurface to the display unit in order to display the image, the lightincidence surface being formed to make contact with a light-emittingsurface through which the light is emitted to the display unit, thelight incidence surface being formed to make an obtuse angle withrespect to the light-emitting surface at a position where the lightincidence surface directly meets the light-emitting surface; a lightemitting unit that emits and provides the light through the lightincidence surface to the light guiding unit, the light emitting unitbeing disposed on the light incidence surface of the light guiding unit;and a light reflecting unit that reflects light which leaks from thelight guiding unit to the display unit, the light reflecting unit beingdisposed on a bottom surface of the light guiding unit.
 31. Thebacklight assembly of claim 30, wherein the light incidence surface andthe light-emitting surface are substantially flat surfaces.